British Journal of Anaesthesia 1997; 77: 50–58
Determinants of splanchnic blood flow
J. TAKALA
The splanchnic region participates in the regulation
of circulating blood volume and systemic blood
pressure [60]. Major reduction of splanchnic blood
volume and flow can be vital in defending the
perfusion of the brain and the heart in acute
hypovolaemia, but prolonged hypoperfusion of the
splanchnic region will inevitably lead to hypoxic
tissue injury [55]. The splanchnic region is also an
important source and target of inflammatory mediators, which have a major impact on both systemic
and regional blood flow and tissue functions [45].
The splanchnic circulation is in close interaction
with the systemic haemodynamics under normal
conditions. In the intensive care patient at risk of
multiple organ failure, there is a complex and poorly
understood interaction between the splanchnic blood
flow, metabolic demands of the tissues and the
mediators of inflammation and vasoregulation.
Inadequate splanchnic blood flow and tissue
perfusion are likely to contribute to the development
of organ failures and increased mortality in various
categories of intensive care patients [8]. Monitoring
of gastric intramucosal pH (pHi) or intramucosal
PCO2 by gastrointestinal tonometry has provided an
indicator of splanchnic tissue perfusion that is
feasible for clinical use in intensive care [15, 18, 19,
27, 30, 32, 47, 48, 49]. Clinical studies using gastrointestinal tonometry have produced evidence to
support the concept of a link between inadequate
splanchnic tissue perfusion and multiple organ
failure.
Gastric intramucosal acidosis, suggesting inadequate splanchnic tissue perfusion, is relatively
common: up to 50 % of patients admitted to
intensive care with signs of circulatory failure, 50 %
of patients undergoing elective cardiac surgery and
18 % of patients undergoing abdominal aortic surgery have at least transient episodes of gastric
intramucosal acidosis [15, 18, 19, 30, 32, 47, 48, 49].
Patients with gastric intramucosal acidosis on admission to intensive care have an increased occurrence of multiple organ failure and increased
mortality [30, 32, 47, 48]. Prevention and treatment
of gastric intramucosal acidosis by administration of
fluids and vasoactive drugs improves the outcome of
(Br. J. Anaesth. 1996; 77: 50–58)
Key words
Blood, flow. Arteries. Oxygen, uptake. Gastrointestinal tract,
blood flow.
those patients with normal pHi on admission [32,
49].
The mechanisms responsible for the increased
morbidity and mortality related to the inadequate
splanchnic perfusion are far from being solved.
Evidently alterations in systemic haemodynamics
can impair the splanchnic blood flow and tissue
perfusion [33, 55]. Tissue hypoxia with consequent
direct hypoxic tissue injury, although likely to
contribute, is clearly a too simplistic explanation.
Translocation of bacteria and toxic substances, as a
result of hypoxic intestinal mucosal injury, may
occur but is unlikely to be a major factor [14].
Inadequate mucosal perfusion increases the intestinal mucosal permeability [20]. All these mechanisms and ischaemia and reperfusion of splanchnic
tissues may contribute to the activation of inflammatory mediator networks, and thereby further
modify the circulatory and metabolic responses
locally, within the splanchnic region and in extrasplanchnic organs [46].
This review discusses the physiology of splanchnic
blood flow, obtained largely from experimental
studies, and the relatively limited available human
data on splanchnic blood flow in patients at risk of
multiple organ failure.
Splanchnic blood flow in normal conditions
The arterial inflow to the splanchnic region is via the
coeliac trunk and the superior and inferior mesenteric arteries [17] (table 1). The venous efflux via
the portal vein represents the sum of all splanchnic
arterial influx, except the hepatic arterial flow. The
venous efflux via the hepatic veins (i.e. the blood
flow through the liver) represents the total hepatosplanchnic bloodflow; inprinciple, the hepaticarterial
flow could be estimated as the difference between
portal venous flow and total hepatic venous efflux.
Hepatic arterial and portal venous blood flow
interact closely. Owing to this “hydrodynamic”
interaction, an alteration of flow to one of the circuits
leads to an opposite change in the other circuit. The
interaction tends to maintain total liver blood flow
constant [57].
The blood flow of the small intestinal villus
deserves special consideration. The artery and vein
of the villus run in parallel but their blood flows are
JUKKA TAKALA, MD, PHD, Critical Care Research Program,
Department of Intensive Care, Kuopio University Hospital, PO
Box 1777, FIN-70211, Kuopio, Finland.
Determinants of splanchnic blood flow
51
Table 1 Arterial blood supply to the splanchnic region (general overview, anatomical variation is common)
Main artery
Main tributary arteries
Main areas supplied
Coeliac trunk
Common hepatic (branches:
right gastric and
gastroduodenal)
Splenic
Liver; parts of stomach, duodenum
and pancreas
Left gastric
Superior mesenteric artery
Inferior mesenteric artery
Inferior pancreaticoduodenal,
intestinal (12–15 branches),
ileocolic, right colic, middle
colic
Left colic, sigmoid, superior
rectal
Spleen; parts of stomach and
pancreas
Parts of stomach and lower
oesophagus
Small intestine, caecum, ascending
colon, most of transverse colon;
parts of duodenum and pancreas
Descending and sigmoid colon;
parts of transverse colon and
rectum
Table 2 Splanchnic and whole body blood flow and oxygen
uptake at rest [6, 24, 57, 77]
Blood flow
(litre min1 m2)
Oxygen consumption
(ml min1 m2)
Oxygen extraction
fraction
Splanchnic
Whole
body
Splanchnic
contribution
to total (%)
0.50–0.80
2.5–4.0
20–30
20–40
110–150
20–35
0.22–0.35
0.22–0.30
MEASUREMENT OF SPLANCHNIC BLOOD FLOW
Figure 1 Schematic presentation of the intestinal villus
countercurrent exchange of oxygen. Oxygen diffuses from the
artery to the villous veins throughout their course to the tip of
the villus. This results in a descending gradient of PO2 from the
base of the villus to the tip.
in opposite directions (fig. 1). The artery forms a
dense capillary network close to the top of the villus.
This anatomical arrangement allows countercurrent
exchange of oxygen from the artery to the vein along
their course within the villus [42]. This results in a
descending gradient of tissue PO2 from the base of
the villus to its tip. This gradient is inversely related
to the blood flow. An alternative explanation for the
tissue PO2 gradient in the villus may be a higher
metabolic activity of the absorptive cells at the tip
[42]. Regardless of the mechanism, the lower PO2 at
the tip may make the villus susceptible to tissue
hypoxia, if vasoconstriction occurs for any reason.
Human studies on splanchnic blood flow are relatively scarce owing to methodological difficulties of
quantitative measurements. Direct measurement of
splanchnic blood flow is practically impossible
without surgery for anatomical reasons (table 1;
multivessel influx and efflux, mixing of portal venous
and hepatic arterial blood within the liver). The
same is true for intravascular pressures within the
splanchnic bed. Accordingly, much of the basic
splanchnic circulatory physiology has been extrapolated from experimental studies and has not been
confirmed in normal humans.
Total hepatosplanchnic blood flow can be estimated according to the Fick principle from the hepatic
uptake of substances that are exclusive metabolized
by the liver and distributed in the plasma [9, 36, 71].
Hepatic venous catheterization is necessary for the
measurement. A detailed description of this technique and its evaluation both in normal subjects and
in intensive care patients has been published [71].
SPLANCHNIC BLOOD FLOW AND OXYGEN UPTAKE
The splanchnic blood flow should be considered in
relation to the splanchnic metabolic activity and the
oxygen extraction capabilities of the splanchnic
tissues. Normally, the total hepatosplanchnic blood
flow is approximately 20–30 % of cardiac output.
Roughly 80 % of the total hepatic blood flow reaches
the liver via the portal vein and 20 % via the hepatic
artery (a tributary of the coeliac trunk). The
splanchnic oxygen consumption at rest is approximately 20–35 % of whole body oxygen consumption.
52
This results in a slightly increased oxygen extraction
fraction, compared with the systemic oxygen extraction at rest [6, 24, 57, 77] (table 2).
When the metabolic demands of the splanchnic
region increase, for example, as the result of feeding,
blood flow to the relevant organs increases in
proportion to the increase in regional oxygen
consumption. Accordingly, the splanchnic oxygen
extraction ratio is well maintained. If the oxygen
extraction is very low, increased extraction may
precede increases in blood flow. The appropriate
increase in splanchnic perfusion can be obtained by
either increased cardiac output or its redistribution,
or by the combination of the two mechanisms [5, 23,
57, 67].
Probably because of its important role in the
regulation of blood volume and redistribution of
blood flow, the splanchnic region has a large capacity
to adapt to reduced blood flow by increasing the
oxygen extraction. During exercise, blood flow is
redistributed from the splanchnic region to the
working muscle [58, 59]. Splanchnic oxygen extraction increases consequently. At least in the short
term, the normal metabolic processes are maintained
at high levels of oxygen extraction. In extreme
conditions, when hypoxia due to reduced inspired
oxygen fraction is superimposed on exercise, splanchnic oxygen extraction may increase to close to
90 %. During this acute experiment, hepatic extraction of indocyanine green decreased, suggesting
that the liver function was deteriorating [58].
The available data in humans suggest that the liver
is well protected against hypoxia in normal subjects,
at least when the exposure is short. On the other
hand, the gut may be more susceptible to develop
local or regional hypoxia. Experimental studies
suggest that the gut may become hypoxic already,
when its oxygen extraction approaches 70 % [50, 78].
CONTROL OF SPLANCHNIC BLOOD FLOW
Gut blood flow
Gut blood flow is regulated by intrinsic and extrinsic
mechanisms. The intrinsic factors include local
metabolic control and myogenic control, local reflexes and locally produced vasoactive substances.
The extrinsic factors include sympathetic innervation, circulating vasoactive substances and systemic haemodynamic changes [23]. The total blood
flow to the gut wall is unevenly distributed in the
four main layers—the mucosa, the submucosa, the
muscularis and the serosa. The mucosa and the
submucosa receive most of the flow, up to 90 %.
Changes in the total gut blood flow may influence the
flow to the different layers to varying extent.
The local metabolic control responds by local
vasodilatation, if blood flow is insufficient for the
local metabolic needs [23, 25]. The actual signal for
the vasodilatation is not known. Both tissue PO2 and
products of cell metabolism have been proposed.
The myogenic control responds to an increase in
vascular transmural pressure by arteriolar vasoconstriction [23, 35]. These two control mechanisms
interact to maintain blood flow adequate for metabolic needs, and to minimize changes in the intestinal
British Journal of Anaesthesia
Figure 2 Effect of feeding on splanchnic blood flow and
oxygen consumption in healthy subjects [data adapted from ref.
34]. A: Peak splanchnic oxygen consumption following a
standard meal (mean (SD)). B: Peak splanchnic blood flow
following a standard meal (mean (SD)).
capillary pressure and transcapillary fluid flux. Nitric
oxide participates the vasoregulation of the hepatosplanchnic bed; its role is discussed separately later.
Intestinal blood pressure–flow autoregulation is
much weaker than the autoregulation of, for example,
renal blood flow [23]. When arterial pressure
decreases, blood flow decreases despite a vasodilatory
response. The autoregulation is enhanced by feeding: the blood flow is better maintained in response
to a decrease in perfusion pressure in the fed state
(i.e. with intraluminal food present) than in the
starved condition.
The response of the intestinal vasculature to an
increase in venous outflow pressure depends on the
adequacy of perfusion [23, 68]. If perfusion is
sufficient for metabolic needs, an increase in the
venous pressure results in arteriolar vasoconstriction
(myogenic control). If perfusion is poor and venous
pressure increases, the vascular resistance decreases
and the capillary density increases (metabolic control).
The gut blood flow has a distinct response to
feeding [23]. Digestion results in pronounced postprandial hyperaemia (fig. 2). Several mechanisms are
probably involved: a local reflex to the presence of
luminal contents, the release of vasoactive gastrointestinal hormones (e.g. gastrin, secretin, cholecystokinin) and the increase in gut metabolism (metabolic
control) [23, 34].
The extrinsic neural control of gut blood flow is
limited primarily to the sympathetic nervous system.
Determinants of splanchnic blood flow
Sympathetic nervous activity reduces gut blood flow
by increasing the vascular resistance of the arteries
and arterioles; the veins have more limited sympathetic innervation. During persisting stimulation,
the blood flow starts to recover after initial reduction
(“autoregulatory escape”) [23, 65]. After the stimulation, blood flow increases transiently to a higher
level than before the stimulation [23].
Catecholamines are the most important circulating
endogenous vasoactive substances that influence the
gut blood flow. Alpha-adrenoceptor stimulation
results in vasoconstriction and beta-adrenoceptor
stimulation in vasodilatation. Accordingly, noradrenaline with predominantly alpha-adrenoceptor
activity can be expected to increase the intestinal
vascular resistance, whereas the effects of adrenaline
are dose-dependent: vasodilatation at low doses and
vasoconstriction at increasing doses when alphastimulation predominates. The net effects of circulating catecholamines on gut blood flow depend on
the concomitant effects on cardiac output [3, 23].
Vasopressin and angiotensin are both potent intestinal vasoconstrictors. Their physiological role in
the control of gut blood flow is not certain. They
may both be involved in the intestinal vasoconstriction in acute hypovolaemia, and also modulate
the response to sympathetic nerve stimulation and
noradrenaline [16, 23].
Hepatic blood flow
There are three principal determinants of hepatic
blood flow. The vascular resistance across the
intestine determines the mesenteric influx and
thereby the portal venous flow. The hepatic arterial
resistance determines the hepatic arterial flow. The
intrahepatic portal venous resistance is less important, since the portal venous flow is mainly
determined by the outflow from the intestine, that is
the resistance across the intestine. Finally, the
hydrodynamic interaction between the hepatic arterial and portal venous flow, as described before,
tends to compensate for any change in one of the
inflows to the liver by a reciprocal change in the
other [6, 57]. The hydrodynamic interaction, also
called the hepatic arterial buffer response, is regulated by adenosine [39].
Autoregulation has little importance in the regulation of hepatic arterial pressure-volume relationship; the relationship between the arterial pressure
and the flow is approximately linear. The hepatic
portal venous bed clearly lacks autoregulation and
has a linear pressure–flow relationship [6, 57].
Sympathetic nervous activity is the principal
neural mechanism that influences hepatic blood flow.
Sympathetic nerve stimulation evokes an increase in
the hepatic arterial and portal resistance. The arterial
vasoconstriction is transient and has similar autoregulatory escape as the intestinal vasoconstriction.
In contrast, the portal response has a slower onset,
but the increase in resistance is sustained, once
established [26, 57]. In addition to the changes in
vascular resistances, sympathetic nerve stimulation
also reduces the hepatic volume, probably via
contraction of the hepatic capacitance vessels. The
53
volume reduction has a slow onset, persists throughout the stimulation and recovers more slowly than it
develops [7, 57].
Role of nitric oxide in splanchnic blood flow
regulation
Recent experimental studies have demonstrated that
nitric oxide is important in the maintenance of basal
vasodilatation in the mesenteric vasculature and the
hepatic artery [2, 44]. In an anaesthetized pig model,
inhibition of nitric oxide synthesis (non-selective
inhibition of both constitutive and inducible nitric
oxide synthase) increased hepatic arterial resistance
but had no effect on the portal vascular resistance,
while the hepatic arterial autoregulation was enhanced. The hydrodynamic interaction between the
hepatic arterial and portal vein blood flow (hepatic
arterial buffer response) was present after nitric
oxide inhibition. After administration of endotoxin,
both the hepatic arterial buffer response and autoregulation were abolished, independent of nitric
oxide. Inhibition of nitric oxide synthesis after
endotoxin increased the resistance of both hepatic
artery and portal vein [2]. This suggests that during
experimental endotoxin shock, nitric oxide is important in preserving the blood flow across the
splanchnic bed. While these observations cannot be
directly extrapolated to human septic shock, they do
suggest that non-selective nitric oxide inhibition in
septic shock may improve blood pressure at the
expense of splanchnic perfusion.
Splanchnic blood flow in patients at risk of
multiple organ failure
Only very few studies with quantitative measurements of splanchnic blood flow in intensive care
patients have been published [1, 10, 11, 22, 28, 29,
52–54, 62, 63, 69, 71–73, 76]. The results have
clearly demonstrated that data obtained from experimental studies or more stable patients should be
extrapolated to the intensive care patient with great
caution. The determinants, clinical relevance and the
time course of splanchnic blood flow abnormalities
in patients at risk of multiple organ failure have not
been well established.
All quantitative splanchnic blood flow studies in
intensive care patients at risk of multiple organ
failure deal with the total hepatosplanchnic blood
flow as measured by the Fick principle [1, 10, 11,
22, 28, 29, 52–54, 62, 63, 69, 71–73, 76]. Gastrointestinal tonometry cannot be used as a surrogate
measure of hepatosplanchnic blood flow, since there
is no consistent relationship between splanchnic
blood flow and measurements obtained by gastric
tonometry [53, 54, 72, 73]. Hence, pHi will be only
discussed briefly in the context of response to therapy
aimed at improving splanchnic perfusion.
The pathophysiology of splanchnic blood flow and
inadequate splanchnic tissue perfusion in intensive
care patients is multifactorial. Two substantially
different patterns of changes in splanchnic blood
flow and metabolic demand are common in intensive
care patients: one observed in low flow states [38, 53,
54
British Journal of Anaesthesia
Figure 3 Splanchnic blood flow and oxygen extraction after
cardiac surgery and in patients with septic shock and
vasopressor therapy [data adapted from refs 62 and 63]. ( )
After cardiac surgery; (●) septic shock vasopressors.
54, 63, 64, 72, 73] and another in severe inflammatory conditions, infections and septic shock [1,
10, 11, 22, 28, 29, 62, 69, 76].
SPLANCHNIC BLOOD FLOW IN LOW FLOW STATES
In low flow states (e.g. cardiogenic shock) and
hypovolaemia (without major injury or sepsis),
splanchnic blood flow decreases without major
changes in splanchnic metabolic demand [53, 54, 63,
72, 73]. In these conditions, perfusion of the heart
and the central nervous system is maintained at the
expense of the peripheral tissues and the splanchnic
region. Once splanchnic vasoconstriction develops
in response to hypovolaemia, the recovery of the
blood flow will be prolonged: the increased splanchnic vascular resistance and reduced blood flow
persists after the circulating blood volume has been
restored and systemic haemodynamics have been
stabilized [16]. This may increase the risk of
inadequate splanchnic perfusion both after resuscitation of hypovolaemia and in intensive care patients
susceptible to acute blood volume changes (e.g. as a
result of capillary leak) [70].
In low flow states, vasoregulation is usually well
preserved and an increased oxyg enextraction compensates for the reduction of blood flow (fig. 3). Fully
developed physiological compensation may preserve
adequate splanchnic tissue oxygenation even during
markedly reduced hepatosplanchnic blood flow. The
limits of compensation and the time of tolerance for
splanchnic hypoperfusion have not been well defined. Perioperative hepatic vein oxygen saturation
below 30 % during liver resection was associated
with postoperative liver dysfunction [37], whereas
brief exposure to lower hepatic venous saturation (or
increased splanchnic oxygen extraction) have been
reported during and after cardiac surgery without
any major consequences [38, 53, 63, 64]. The splanchnic blood is defended at the expense of peripheral
blood flow in low cardiac output syndrome after
cardiac surgery [53, 63].
Nevertheless, prolonged hypovolaemia or low
cardiac output will inevitably lead to splanchnic
tissue hypoxia and increase the risk of multiple organ
Figure 4 Increased splanchnic oxygen demand and blood flow
in sepsis. A: Splanchnic hypermetabolism tends to increase with
increasing severity of sepsis [data adapted from refs 11, 62 and
76]. B: Splanchnic blood flow and the severity of sepsis [data
adapted from refs 11, 62 and 76].
failure. It is reasonable to assume that a slowly
developing low splanchnic blood flow is better
tolerated than an acute reduction.
SPLANCHNIC BLOOD FLOW IN INFLAMMATION AND
INFECTION
In severe inflammation (e.g. systemic inflammatory
response syndrome or SIRS, septic infections, septic
shock), the metabolic demand for oxygen in the
splanchnic region is increased [1, 10, 11, 22, 28, 29,
62, 69, 76]. In patients with normal or hyperdynamic
haemodynamics, the total splanchnic blood flow is
also higher than normal, but the increase in oxygen
consumption is disproportionate to the increase in
blood flow, and necessitates high oxygen extraction
(figs 3 and 4). This appears to be the case regardless
of whether stable haemodynamics have been obtained by fluids alone or with the aid of vasoactive
Determinants of splanchnic blood flow
55
Figure 5 Changes in splanchnic blood flow in septic shock in
response to treatment of hypotension with vasopressors [data
adapted from ref. 62]. Wide interindividual variability is
characteristic of the response.
Figure 6 Changes in splanchnic blood flow in response to
dobutamine after cardiac surgery [data adapted from ref. 53].
Splanchnic blood flow changes parallel the changes in cardiac
output.
drugs [1, 10, 11, 22, 28, 29, 62, 69, 76]. In hyperdynamic septic shock during hypotension, splanchnic blood flow and splanchnic oxygen consumption
are higher than normal and the splanchnic oxygen
extraction is high [62]. Correction of hypotension by
vasopressor drugs tends to increase the splanchnic
blood flow further in hyperdynamic septic shock,
although individual responses may vary (fig. 5) [62].
Endothelial injury is common in sepsis and
contributes to abnormal vascular tone, blood flow
maldistribution and development of hypovolaemia
[8, 14, 46]. In addition, severe sepsis is almost
invariably accompanied by acute respiratory failure,
which limits the systemic oxygen delivery. Myocardial depression is also common in sepsis and
many limit the response of systemic blood flow to the
increased oxygen demand [51]. Under these circumstances, the splanchnic hypermetabolism increases the risk of splanchnic oxygen delivery/
demand mismatch, and even subtle changes in blood
volume, cardiac output, arterial oxygenation or
oxygen demand in other tissues may lead to an
imbalance between splanchnic oxygen delivery and
demand.
Adrenergic agents
THERAPEUTIC INTERVENTIONS AND SPLANCHNIC
BLOOD FLOW
Volume resuscitation
The blood volume can be expected to have a major
impact on splanchnic blood flow [13, 16, 55]. Indeed,
reduction of splanchnic blood flow has been demonstrated in normal subjects after controlled smallvolume haemorrhage [12, 56], and after simulated
hypovolaemia following the application of lower
body negative pressure [16]. Restoration of blood
volume after simulated hypovolaemia was associated
with a protracted reduction of splanchnic blood flow.
Effects of blood volume on splanchnic blood flow in
intensive care patients have not been published.
Indirect data from studies using volume resuscitation
to improve gastric pHi suggests that restoration of
blood volume is of primary importance in assuring
adequate splanchnic perfusion in intensive care
patients [32, 47–49].
Vasoactive drugs, especially sympathomimetic
amines are used frequently to support tissue perfusion in circulatory failure. The effects of sympathomimetic drugs on splanchnic blood flow in intensive
care patients can not be predicted from their
pharmacological characteristics alone or extrapolated
from experimental models. Traditionally, the potential effects of adrenergic agents on regional
perfusion have been interpreted in terms of their
relative adrenergic receptor activity. In critically ill
patients, the effects may be modified, for example as
the result of receptor downregulation. In experimental studies, alpha-adrenergic stimulation by
dopamine, noradrenaline and adrenaline increase
renal and visceral vascular resistance and reduce
renal and visceral blood flow [61]. The effects of
dobutamine depend on the balance between its
alpha-mediated vasoconstriction and beta-mediated
vasodilation [74]. Dopexamine with beta2and dopaminergic properties and without alphastimulation may have beneficial effects on
splanchnic blood flow [41].
In 10 patients with septic shock, correction of
hypotension by administration of vasopressor doses
of dopamine increased splanchnic blood flow,
whereas the effects of noradrenaline were more
variable [62]. On the other hand, dopamine
worsened gastric mucosal acidosis in septic shock,
while noradrenaline resulted increased gastric
mucosal pH despite identical effects on systemic
haemodynamics [43].
In patients with chronic congestive heart failure,
dopexamine increased the splanchnic blood flow
whereas neither dopamine nor dobutamine had an
effect [40]. In contrast, both dobutamine and
dopexamine consistently increased splanchnic blood
flow immediately after cardiac surgery (figs 6 and 7)
[53, 63, 72]. Despite the major increases in total
splanchnic blood flow, both dobutamine and dopexamine lowered the gastric pHi or failed to correct
the gastric mucosal acidosis [53, 72]. These effects
were even more prominent in patients with low
cardiac output [53]. On the other hand, dobutamine
corrected gastric mucosal acidosis in patients with
56
British Journal of Anaesthesia
splanchnic flow in cardiac failure [40]. After cardiac
surgery, enalapril had no effect on either cardiac
output or hepatosplanchnic blood flow, but reduced
the gastric pHi [52].
The effect of vasodilators on hepatosplanchnic
blood flow or gastric pHi have not been studied in
septic patients. Nevertheless, the available data
suggest that also the effects of vasodilators are
modified markedly by the underlying clinical condition. It seems likely that redistribution of blood
flow may occur at the level of both macro- and
microcirculation.
References
Figure 7 Changes in splanchnic blood flow and gastric pHi in
response to dobutamine after cardiac surgery [data adapted
from ref. 53]. Gastric mucosal acidosis worsens especially in
patients with low cardiac output despite the increased
splanchnic blood flow.
sepsis [31]. Evidently, the underlying disease can
modify the splanchnic blood flow responses to
vasoactive drugs.
The cause for the decrease in gastric pHi despite
increased blood flow is not clear. The effects of a
vasoactive drug may not be uniform throughout the
splanchnic region: vasopressor therapy with dopamine or noradrenaline in experimental endotoxin
shock increases regional vascular resistance of the
colon, while the perfusion in the other parts of
splanchnic region is well maintained [4]. The effects
of vasoactive drugs on microcirculation may differ
despite similar effects on blood flow distribution in
major vessels [21]. Observations in experimental
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dobutamine produced more hepatocellular damage
compared with dopexamine [75]. The catecholamines may also markedly modify the activity of
various metabolic pathways in the liver [3] and
simultaneously alter the splanchnic blood flow and
its distribution. Accordingly, catecholamines may
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balance between regional oxygen delivery and tissue
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Non-adrenergic vasodilators
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output in postoperative cardiac surgery patients [54].
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pHi decreased slightly.
Angiotensin converting enzyme inhibitors either
had no effect or slightly reduced the hepato-
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